The research plan for the renewal period will include: review and verification of the staging of all gastrointestinal malignancies, including continuation of the annual follow-up and review of all deaths; measurement of the sensitivity and specificity of the guaiac slide test for detection of predictive value of the test; examination of the problem of length bias; and analysis of dietary data. Surveillance of the enrolled population will include examination of the post-screening behaviors of the screened groups in continuing use of guaiac testing.